Temperature control system and method

ABSTRACT

A temperature control system for a frame ( 20 ) including a thermal electric cooling (TEC) element ( 32 ) having a first face ( 34 ) and a second face ( 36 ), the TEC element ( 32 ) disposed to form a gap ( 50 ) between the first face ( 34 ) and the frame ( 20 ), and a fluid heat transfer element ( 38 ) thermally connected to the second face ( 36 ). The temperature control system also employs a thermal group, a flushable reservoir, and/or a phase change element, as desired.

This invention relates generally to metrology and manufacturing systems,and more specifically to metrology and manufacturing system temperaturecontrol.

Metrology systems are increasingly important as component sizes declineand precision requirements increase. The component under test must beheld stationary throughout the measurement to provide accuratemeasurement. The component rests on a metrology frame, which must bedimensionally stable and vibration free to provide a stable geometricreference for the physical measurement. Problems arise, however, whenthe metrology frame includes or is in contact with a heat source causingthermal expansion in the metrology frame, or includes or is in contactwith a vibration source.

Attempting to cure the thermal expansion problem can give rise to thevibration problem. For example, one approach to maintain the temperatureof the metrology frame is to pump fluid at a precisely controlledtemperature through holes in the metrology frame. The fluid flow inducesvibrations in the metrology system reducing the accuracy. Therefore, itis necessary to trade off temperature control for vibration control.

Other problems occur with heat sources in or on the metrology frame.More than one heat source can be present on or in the metrology frame.This causes complex distortions of the metrology frame, which cannot beaccounted for through simple post-measurement correction. The heatproduction of the heat source can also be a function of time. Forexample, when the heat source is a drive motor, the drive motor producesthe most heat when it is driving, changing temperature as it is turnedon and off. Controlling the metrology frame temperature through coolingfluid temperature limits the ability to adapt to such changingconditions. The cooling fluid temperature must also be preciselycontrolled throughout the measurement to avoid introducing uncertainty.

Similar problems occur with other precision manufacturing operationsrequiring a dimensionally stable and vibration free work frame, such asoptical semiconductor processing using wafer steppers and precisionmachining using precision milling machines.

It would be desirable to have a metrology system temperature controlthat overcomes the above disadvantages.

One aspect of the present invention provides a temperature controlsystem for a frame, including a thermal electric cooling (TEC) elementhaving a first face and a second face, the TEC element disposed to forma gap between the first face and the frame, and a fluid heat transferelement thermally connected to the second face.

Another aspect of the present invention provides a temperature controlsystem for a frame, including a thermal electric cooling (TEC) elementhaving a first face and a second face, and a thermal group including athermal device and a fluid heat transfer element, the thermal devicebeing thermally connected to the fluid heat transfer element, whereinthe first face is thermally connected to the frame and the second faceis thermally connected to the thermal group.

Another aspect of the present invention provides a temperature controlsystem for a frame, including a thermal electric cooling (TEC) elementhaving a first face and a second face, and a fluid heat transfer elementhaving a flushable reservoir, wherein the first face is thermallyconnected to the frame and the second face is thermally connected to thefluid heat transfer element.

Another aspect of the present invention provides a method of temperaturecontrol for a frame, including providing a thermal electric cooling(TEC) element and a fluid heat transfer element thermally connected tothe TEC element, locating the TEC element near the frame to form a gap,and controlling the TEC element to transfer heat across the gap.

Another aspect of the present invention provides a temperature controlsystem for a frame including a thermal electric cooling (TEC) elementhaving a first face and a second face, a phase change element, and afluid heat transfer element, wherein the first face is thermallyconnected to the frame and the second face is thermally connected to thephase change element, and the phase change element is thermallyconnected to the fluid heat transfer element.

The foregoing and other features and advantages of the invention willbecome further apparent from the following detailed description of thepresently preferred embodiment, read in conjunction with theaccompanying drawings. The detailed description and drawings are merelyillustrative of the invention rather than limiting, the scope of theinvention being defined by the appended claims and equivalents thereof.

FIGS. 1 & 2 are schematic diagrams of a temperature control systememploying a gap made in accordance with the present invention;

FIGS. 3-6 are schematic diagrams of a temperature control systememploying a thermal group made in accordance with the present invention;

FIG. 7 is a schematic diagram of a temperature control system employinga flushable reservoir made in accordance with the present invention;

FIG. 8 is a schematic diagram of a temperature control system employinga phase change element made in accordance with the present invention;and

FIG. 9 is a schematic diagram of an operational control system for atemperature control system made in accordance with the presentinvention.

FIGS. 1 & 2 are schematic diagrams of a temperature control systememploying a gap made in accordance with the present invention. Thetemperature control system is separated from the frame by a gap, whichavoids vibration from the temperature control system being transferredto the frame. Heat is exchanged between the temperature control systemand the frame across the gap by radiative and/or conductive heattransfer.

Referring to FIG. 1, frame 20 includes a thermal device 22, such as aheat source or cold source. Temperature control system 30 includesthermal electric cooling (TEC) elements 32 and a fluid heat transferelement 38. The TEC elements 32 each have a first face 34 disposedtoward the frame 20 and a second face 36 thermally connected to thefluid heat transfer element 38. A temperature controller (not shown)provides a TEC control signal to the TEC elements 32 to control heattransfer across the TEC elements 32. Temperature sensor 68 thermallyconnected to the frame 20 provides a measured frame temperature signalto the operational control system. The fluid heat transfer element 38includes a fluid passage 40 permitting flow of a temperature controlfluid, which is controlled by valve 72. The frame 20 is separated fromthe temperature control system 30 by gap 50. In one embodiment, a TECradiative coating 52 and/or a frame radiative coating 54 are disposed onthe first face 34 of the TEC elements 32 and/or the frame 20,respectively, to promote heat transfer across the gap 50. In analternative embodiment, no radiative coating is used.

The frame 20 is any frame for which dimensional stability and freedomfrom vibration are required, such as a metrology frame, semiconductorwafer stepper, precision milling machine stage, or the like. The thermaldevice 22 can be associated with operation and control of the frame 20,such as a motor, drive system, hydraulic lines, or the like. The thermaldevice 22 can also be a specimen or workpiece being examined or workedon the frame 20, or heating, cooling, motion, or control equipmentassociated with the specimen or workpiece. The thermal device 22 can bein direct contact with the frame 20 and exchange heat with the frame 20by conduction, or can be near the frame 20 and exchange heat with theframe 20 by radiation and/or convection.

The TEC elements 32 are thermoelectric coolers, also known as Peltiercoolers. The TEC elements 32 act as heat pumps, moving heat from oneface to the other in response to a DC current TEC control signal. Thedirection of heat flow through the TEC elements 32 can be reversed byreversing the polarity of the DC current TEC control signal, providingprecise temperature control. A typical TEC element includessemiconductor material between plates forming the faces. The TECelements 32 can be a single TEC element or a number of individual TECelements.

The gap 50 is of any width permitting radiative heat transfer betweenthe frame 20 and the temperature control system 30. Avoiding contactbetween the frame 20 and the temperature control system 30 preventsvibrations from the temperature control system 30, such as vibrationsfrom the fluid flow through the fluid heat transfer element 38, fromtransferring to the frame 20. The gap 50 can be large or small, asdesired. In one embodiment, the gap 50 is about 4 millimeters or larger.

The fluid heat transfer element 38 exchanges heat with the TEC elements32 and transfers the heat to the temperature control fluid flowingthrough the fluid passage 40. The fluid heat transfer element 38 caninclude internal and/or external fins to further promote heat transferfrom the temperature control fluid to the fluid heat transfer element 38or from the fluid heat transfer element 38 to the surroundingenvironment. The temperature control fluid flowing through the fluidpassage 40 can be water, oil, or any other fluid suitable for thetemperature range of intended use. The valve 72, such as a stop valve ora flow control valve, controls flow of the temperature control fluidthrough the fluid passage 40. In one embodiment, the fluid passage 40can include a flushable reservoir allowing rapid exchange of thetemperature control fluid within the flushable reservoir. In analternative embodiment, the flow of the temperature control fluid withinthe fluid passage 40 can be shut off during the measurement ormanufacturing process on the frame 20 to further reduce any disturbancesnear the frame 20.

The optional TEC radiative coating 52 and frame radiative coating 54 arehigh emissivity, high thermal conductivity coatings to promote radiativeheat transfer between the frame 20 and the temperature control system 30across the gap 50. The coatings can be any high emissivity, highconductivity coating, such as those used in vacuum or solarapplications, including metallic oxide coatings, glass (Si02) coatings,or ceramic coatings. In one embodiment, the coatings are applieddirectly to the respective faces of the frame 20 and the fluid heattransfer element 38. In an alternative embodiment, the coatings areapplied to an additional layer, such as a copper plate, and theadditional layer applied to the respective faces of the frame 20 and thefluid heat transfer element 38.

Referring to FIG. 2, in which like elements share like reference numberswith FIG. 1, the temperature control system 30 controls the temperaturelocally by exchanging heat with the thermal device 22 directly. The gap50 is formed about the thermal device 22. In one embodiment, the TECradiative coating 52 and/or a frame radiative coating 54 are disposed onthe first face 34 of the TEC elements 32 and/or the thermal device 22,respectively, to promote heat transfer across the gap 50.

In operation, the temperature control system 30 exchanges heat with theframe 20 and/or the thermal device 22 to maintain the frame 20 at aconstant temperature. For metrology applications, the temperature of theframe 20 is held stable to maintain a constant geometry for the frame20: the absolute temperature of the frame 20 is not critical. Formanufacturing and biological applications, the temperature of the frame20 is held at the desired temperature required by the process. Thetemperature sensor 68 thermally connected to the frame 20 provides anindication of the frame temperature. The temperature sensor 68 can bephysically located anywhere on the frame 20 or fluid heat transferelement 38 that provides a suitable temperature measurement for theoperational control system. As discussed in connection with FIG. 8below, the control of the heat flow through the TEC elements 32 can usefeedback control on temperature error and can optionally use feedforward control anticipating thermal load from the thermal device 22. Inone embodiment, the flow rate and/or temperature of the temperaturecontrol fluid through the fluid heat transfer element 38 can be variedto provide additional temperature control.

FIGS. 3-6, in which like elements share like reference numbers with eachother and with FIG. 1, are schematic diagrams of a temperature controlsystem employing a thermal group made in accordance with the presentinvention. The temperature control system employs a thermal groupincluding a thermal device, which is associated with the frame, and afluid heat transfer element.

Referring to FIG. 3, temperature control system 30 includes thermalelectric cooling (TEC) elements 32 and a thermal group 60. The TECelements 32 each have a first face 34 thermally connected to the frame20 and a second face 36 thermally connected to the thermal group 60. Thethermal group 60 includes a thermal device 22, such as a heat source orcold source, associated with the frame 20 and a fluid heat transferelement 38. The thermal device 22 is mechanically connected to the frame20, with the TEC elements 32 disposed between the thermal device 22 andthe frame 20 in the embodiment illustrated. In one embodiment, thethermal device 22 is adjacent to the TEC elements 32, the fluid heattransfer element 38 is further away from the frame 20 than the thermaldevice 22, and the thermal device 22 is thermally connected to thesecond face 36. In an alternative embodiment, the fluid heat transferelement 38 is adjacent to the TEC elements 32, the thermal device 22 isfurther away from the frame 20 than the fluid heat transfer element 38,and the fluid heat transfer element 38 is thermally connected to thesecond face 36. A temperature controller (not shown) provides a TECcontrol signal to the TEC elements 32 to control heat transfer acrossthe TEC elements 32 between the frame 20 and the thermal group 60. TheTEC elements 32 provide perfect insulation of the frame 20 by zeroingout heat transfer with the frame 20.

Referring to FIG. 4, the temperature control system 30 includes mountingpads 62 located between the thermal group 60 and the frame 20, inparallel with the TEC elements 32. The mounting pads 62 allow a firmmechanical connection between the thermal group 60 and the frame 20,while the TEC elements 32 manage heat transfer between the thermal group60 and the frame 20.

In the embodiment illustrated in FIG. 5, the frame 20 includes aninsulating layer 64 and a conducting layer 66 with the conducting layer66 disposed on the insulating layer 64. The conducting layer 66 isthermally connected to the first face 34 of the TEC elements 32. Theconducting layer 66 includes a temperature sensor 68 thermally connectedto the conducting layer 66 to generate a measured frame temperaturesignal. The conducting layer 66 provides a homogeneous indication offrame temperature by being highly conductive, better smoothing out localtemperature variations. The conducting layer 66 can be any material withhigh thermal conductivity, such as aluminum, copper, or the like. Theinsulating layer 64 can be any material with low thermal conductivity,such as plastic, ceramic, foam, or the like.

In the embodiment illustrated in FIG. 6, the frame 20 includes theinsulating layer 64 and the conducting layer 66, with mounting pads 62located between the thermal group 60 and the conducting layer 66 inparallel with the TEC elements 32. The mounting pads 62 allow a firmmechanical connection between the thermal group 60 and the frame 20,while the TEC elements 32 manage heat transfer between the thermal group60 and the frame 20.

FIG. 7 is a schematic diagram of a temperature control system employinga flushable reservoir made in accordance with the present invention. Theflushable reservoir allows rapid replacement of the temperature controlfluid to provide fresh heat transfer capacity.

Temperature control system 30 includes thermal electric cooling (TEC)elements 32 and a fluid heat transfer element 38. The fluid heattransfer element 38 includes a body 74 and a fluid passage 40. Flushablereservoir 70 is included in the fluid passage 40 of the fluid heattransfer element 38 and contains the temperature control fluid (notshown). Valve 72 controls the flow through the fluid passage 40.Typically, the heat capacity of the temperature control fluid in theflushable reservoir 70 is larger than the heat capacity of the body 74of the fluid heat transfer element 38, so that the temperature controlfluid in the flushable reservoir 70 acts as the heat source or heat sinkfor the TEC elements 32. The temperature control fluid is flushed fromthe flushable reservoir 70 and replaced by fresh temperature controlfluid, so that the heat source or heat sink is replenished for the nextuse.

In operation, the flushable reservoir 70 is filled and the valve 72 isshut to avoid any flow vibrations from the fluid heat transfer element38 which could be transferred to the frame 20. The temperature controlsystem 30 exchanges heat with the frame 20 through the TEC elements 32.The temperature of the temperature control fluid increases or decreasesdepending on whether the flushable reservoir 70 is a heat sink or heatsource. When the temperature of the temperature control fluid reaches alimit, or the measuring or monitoring operation requiring minimalvibration has been completed, the valve 72 is opened to rapidly flushthe temperature control fluid from the flushable reservoir 70 and toprovide fresh temperature control fluid. The valve 72 is closed and thefluid heat transfer element 30 is ready for the next use. Those skilledin the art will appreciate that the flushable reservoir 70 can be usedwith any of the temperature control systems described herein.

FIG. 8 is a schematic diagram of a temperature control system employinga phase change element made in accordance with the present invention.The phase change element acts as a thermal reservoir, allowing flowthrough the fluid heat transfer element to be shut off when minimalframe vibration is required.

Temperature control system 30 includes thermal electric cooling (TEC)elements 32, phase change element 76, and fluid heat transfer element38. The TEC elements 32 are thermally connected to the frame 20 and thephase change element 76. The phase change element 76 is thermallyconnected to the fluid heat transfer element 38, which includes a fluidpassage 40 for flow of a temperature control fluid. Valve 72 controlsthe flow through the fluid passage 40. The phase change element 76includes phase change materials which change phase at or near theoperating temperature of the TEC elements 32. In one embodiment, thefluid heat transfer element 38 is included as part of and incorporatedwithin the phase change element 76 to increase the heat transfer betweenthe phase change materials and the temperature control fluid.

The phase change in the phase change element 76 can be any phase changethat absorbs or releases heat as desired for a particular application,such as a solid-liquid transition (heat of fusion), liquid-gastransition (heat of vaporization), or solid-gas transition (heat ofsublimation). Examples of phase change materials that can be used in thephase change element 76 include water; salt hydrate, such as potassiumfluoride tetrahydrate (KF.4H₂O) or calcium chloride hexahydrate(CaCl₂.6H₂O); or a eutectic mixture, such as a salt-water mixture, likea sodium chloride (NaCl)-water mixture. Those skilled in the art willappreciate that a number of phase change materials are suitable for usein the phase change element 76 depending on the particular phase changetemperature desired. For example, salt hydrate can be used around roomtemperature and a salt-water eutectic mixture can be used around a lowtemperature of about −20 degrees C.

In operation, the valve 72 is shut to avoid any flow vibrations from thefluid heat transfer element 38 which could be transferred to the frame20. The temperature control system 30 exchanges heat with the frame 20through the TEC elements 32. The phase change materials in the phasechange element 76 change phase in response to the heat transfer with theTEC elements 32. When the measuring or monitoring operation requiringminimal vibration has been completed, the valve 72 is opened to providetemperature control fluid through the fluid passage 40. The phase changematerials return to their initial state and the phase change element 76is ready for the next use. Those skilled in the art will appreciate thatthe the phase change element 76 can be used with any of the temperaturecontrol systems described herein.

FIG. 9, in which like elements share like reference numbers with FIG. 1,is a schematic diagram of a operational control system for a temperaturecontrol system made in accordance with the present invention. Theoperational control system provides a TEC control signal to the TECelements to control heat transfer across the TEC elements.

The operational control system 100 includes a temperature sensor 68being thermally connected to the frame and generating a measured frametemperature signal 102. In one embodiment, a number of temperaturesensors can be a thermally connected to the frame and their outputscombined so that the measured frame temperature signal indicates anaverage or weighted average frame temperature. A desired temperatureT_set 104 is set manually or determined by another control system and adesired temperature signal 106 generated. The measured frame temperaturesignal 102 and the desired temperature signal 106 are compared atcomparator 108 and a temperature difference signal 110 generated. Atemperature controller 112 is responsive to the temperature differencesignal 110 and generates a TEC control signal 114, which controls heatflow through the TEC elements 32.

In one embodiment, the temperature controller 112 is additionallyresponsive to a thermal device signal 118, providing feed forwardcontrol. A thermal device controller 116 controls the thermal device 22,such as a motor or drive system. The thermal device controller 116generates the thermal device signal 118, which is provided to both thethermal device 22 and the temperature controller 112. The temperaturecontroller 112 adjusts the TEC control signal 114 to anticipate thechange in heat load to the frame from any change in operation of thethermal device 22. The temperature controller 112 can include modelingof the thermal transient response of the frame and the thermal device 22to account for lag between the control signal and the thermal response.Those skilled in the art will appreciate that the operational controlsystem 100 can be used with any of the temperature control systemsdescribed herein.

While the embodiments of the invention disclosed herein are presentlyconsidered to be preferred, various changes and modifications can bemade without departing from the scope of the invention. The scope of theinvention is indicated in the appended claims, and all changes that comewithin the meaning and range of equivalents are intended to be embracedtherein.

1. A temperature control system for a frame 20 comprising: a thermalelectric cooling (TEC) element 32, the TEC element 32 having a firstface 34 and a second face 36, the TEC element 32 disposed to form a gap50 between the first face 34 and the frame 20; and a fluid heat transferelement 38, the fluid heat transfer element 38 being thermally connectedto the second face
 36. 2. The system of claim 1 further comprising a TECradiative coating 52 disposed on the first face
 34. 3. The system ofclaim 1 wherein the frame 20 has a frame radiative coating
 54. 4. Thesystem of claim 1 wherein the frame 20 has a thermal device 22 and thegap 50 is formed about the thermal device
 22. 5. The system of claim 1further comprising: a temperature sensor 68, the temperature sensor 68being thermally connected to the frame 20 and generating a measuredframe temperature signal 102; a comparator 108, the comparator 108determining a difference between the measured frame temperature signal102 and a desired temperature signal 106, and generating a temperaturedifference signal 110; and a temperature controller 112, the temperaturecontroller 112 being responsive to the temperature difference signal 110and generating a TEC control signal 114; wherein the TEC element 32 isresponsive to the TEC control signal
 114. 6. The system of claim 5wherein the frame 20 has a thermal device 22, further comprising: athermal device controller 116, the thermal device controller 116operably connected to control the thermal device 22, and generating athermal device signal 118; wherein the temperature controller 112 isadditionally responsive to the thermal device signal
 118. 7. The systemof claim 1 wherein the fluid heat transfer element 38 has a flushablereservoir
 70. 8. The system of claim 1 wherein the fluid heat transferelement 38 has a fluid passage 40 and a valve 72 connected to controlflow through the fluid passage 40, the valve 72 being selected from thegroup consisting of a stop valve and a flow control valve.
 9. Atemperature control system for a frame 20 comprising: a thermal electriccooling (TEC) element 32, the TEC element 32 having a first face 34 anda second face 36; and a thermal group 60, the thermal group 60 having athermal device 22 and a fluid heat transfer element 38, the thermaldevice 22 being thermally connected to the fluid heat transfer element38; wherein the first face 34 is thermally connected to the frame 20 andthe second face 36 is thermally connected to the thermal group
 60. 10.The system of claim 9 wherein the thermal device 22 is thermallyconnected to the second face
 36. 11. The system of claim 9 wherein thefluid heat transfer element 38 is thermally connected to the second face36.
 12. The system of claim 9 further comprising a mounting pad betweenthe thermal group 60 and the frame 20 in parallel with the TEC element32.
 13. The system of claim 9 wherein the frame 20 has an insulatinglayer 64 and a conducting layer 66, wherein the conducting layer 66 isdisposed on the insulating layer 64, and the conducting layer 66 isthermally connected to the first face
 34. 14. The system of claim 13further comprising a mounting pad 62 between the first face 34 and theframe 20 in parallel with the TEC element
 32. 15. The system of claim 13further comprising a temperature sensor 68 thermally connected to theconducting layer 66, the temperature sensor generating 68 a measuredframe temperature signal.
 16. The system of claim 9 further comprising:a temperature sensor 68, the temperature sensor 68 being thermallyconnected to the frame 20 and generating a measured frame temperaturesignal 102; a comparator 108, the comparator 108 determining adifference between the measured frame temperature signal 102 and adesired temperature signal 106, and generating a temperature differencesignal 110; and a temperature controller 112, the temperature controller112 being responsive to the temperature difference signal 110 andgenerating a TEC control signal 114; wherein the TEC element 32 isresponsive to the TEC control signal
 114. 17. The system of claim 16wherein the frame 20 has a thermal device 22, further comprising: athermal device controller 116, the thermal device controller 116operably connected to control the thermal device 22, and generating athermal device signal 118; wherein the temperature controller 112 isadditionally responsive to the thermal device signal
 118. 18. The systemof claim 9 wherein the fluid heat transfer element 38 has a flushablereservoir
 70. 19. The system of claim 9 wherein the fluid heat transferelement 38 has a fluid passage 40 and a valve 72 connected to controlflow through the fluid passage 40, the valve 72 being selected from thegroup consisting of a stop valve and a flow control valve.
 20. Atemperature control system for a frame 20 comprising: a thermal electriccooling (TEC) element 32, the TEC element 32 having a first face 34 anda second face 36; and a fluid heat transfer element 38, the fluid heattransfer element 38 having a flushable reservoir 70; wherein the firstface 34 is thermally connected to the frame 20 and the second face 36 isthermally connected to the fluid heat transfer element
 38. 21. Thesystem of claim 20 further comprising: a temperature sensor 68, thetemperature sensor 68 being thermally connected to the frame 20 andgenerating a measured frame temperature signal 102; a comparator 108,the comparator 108 determining a difference between the measured frametemperature signal 102 and a desired temperature signal 106, andgenerating a temperature difference signal 110; and a temperaturecontroller 112, the temperature controller 112 being responsive to thetemperature difference signal 110 and generating a TEC control signal114; wherein the TEC element 32 is responsive to the TEC control signal114.
 22. The system of claim 21 wherein the frame 20 has a thermaldevice 22, further comprising: a thermal device controller 116, thethermal device controller 116 operably connected to control the thermaldevice 22, and generating a thermal device signal 118; wherein thetemperature controller 112 is additionally responsive to the thermaldevice signal
 118. 23. The system of claim 20 wherein the fluid heattransfer element 38 has a valve 72 connected to control flow through theflushable reservoir 70, the valve 72 being selected from the groupconsisting of a stop valve and a flow control valve.
 24. A method oftemperature control for a frame comprising: providing a thermal electriccooling (TEC) element and a fluid heat transfer element thermallyconnected to the TEC element; locating the TEC element near the frame toform a gap; and controlling the TEC element to transfer heat across thegap.
 25. A temperature control system for a frame 20 comprising: athermal electric cooling (TEC) element 32, the TEC element 32 having afirst face 34 and a second face 36; a phase change element 76; and afluid heat transfer element 38; wherein the first face 34 is thermallyconnected to the frame 20 and the second face 36 is thermally connectedto the phase change element 76, and the phase change element 76 isthermally connected to the fluid heat transfer element
 38. 26. Thesystem of claim 25 further comprising: a temperature sensor 68, thetemperature sensor 68 being thermally connected to the frame 20 andgenerating a measured frame temperature signal 102; a comparator 108,the comparator 108 determining a difference between the measured frametemperature signal 102 and a desired temperature signal 106, andgenerating a temperature difference signal 110; and a temperaturecontroller 112, the temperature controller 112 being responsive to thetemperature difference signal 110 and generating a TEC control signal114; wherein the TEC element 32 is responsive to the TEC control signal114.
 27. The system of claim 26 wherein the frame 20 has a thermaldevice 22, further comprising: a thermal device controller 116, thethermal device controller 116 operably connected to control the thermaldevice 22, and generating a thermal device signal 118; wherein thetemperature controller 112 is additionally responsive to the thermaldevice signal
 118. 28. The system of claim 25 wherein the fluid heattransfer element 38 has a valve 72 connected to control flow through theflushable reservoir 70, the valve 72 being selected from the groupconsisting of a stop valve and a flow control valve.
 29. The system ofclaim 25 wherein the phase change element 76 comprises a phase changematerial selected from the group consisting of water, salt hydrate,potassium fluoride tetrahydrate, calcium chloride hexahydrate, aeutectic mixture, a salt-water mixture, and a sodium chloride-watermixture.